American Society of Civil Engineers

Effect of 1D Infiltration Assumption on Stability of Spatially Variable Slope

by Anastasia M. Santoso, (Ph.D student, Department of Civil & Environmental Engineering, National University of Singapore, Blk E1A, #07-03, 1 Engineering Drive 2, Singapore 117576. E-mail:, Kok-Kwang Phoon, F.ASCE, (Professor, Department of Civil & Environmental Engineering, National University of Singapore.), and Ser-Tong Quek, (Professor, Department of Civil & Environmental Engineering, National University of Singapore.)
Section: Risk and Reliability in Geoenvironmental Engineering, pp. 704-711, (doi:

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Document type: Conference Proceeding Paper
Part of: Geo-Risk 2011: Risk Assessment and Management
Abstract: Rainfall-induced landslides are often analyzed using the infinite slope model, in which each slice of the slope is treated as a soil column subjected to one-dimensional, vertical infiltration. This one-dimensional (1D) assumption means that slope inclination and lateral downslope flow of water are ignored. Some studies have shown that the impact of lateral flow on slope stability is not significant. Hence, 1D infiltration analysis is sufficient to analyze rainfall-induced landslides. However, those studies are based on homogeneous soils, i.e. soil spatial variability is not considered in the analysis. This paper investigates the significance of slope inclination and lateral flow on the stability of an infinite slope with spatially varying soil in the depth direction. Only the saturated hydraulic conductivity of the soil is assumed to be spatially varying in the form of a stationary lognormal random field. It was found that the impact of the inclination on the pressure head and the factor of safety is not significant. However, the impact on the probability of slope failure is significant for some examples studied in this paper.

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